Generally, composite articles formed of an elastomeric base material and reinforcing fibers are common in the art. The reinforcing fibers impart improved mechanical properties, such as abrasion resistance, tensile strength, compression resistance, and the like to the composite article. The fiber distribution and orientation are important factors which affect such properties. Controlling fiber orientation, therefore, is an important consideration in order to provide a composite article having the desired mechanical properties.
There are known techniques for orienting reinforcing fibers in an elastomeric material. However, in many processes the fibers are generally oriented in a direction consistent with and parallel to the initial material flow direction. A problem encountered in the art relates to orienting reinforcing fibers in a composite article in a direction which differs from the material flow and especially in a direction perpendicular thereto.
One method proposed to orient fibers in a composite article in a direction which varies from the material flow is disclosed in U.S. Pat. No. 5,156,907 wherein a heated mixture of molding compound (glass) and fibers (carbon) is injected through an elongated injection port into a die. The injection port has a thickness which is purported to be between 30%-70% of the die thickness. The optimum fiber length is 0.5 inches (1.27 cm) for the particular carbon fiber/glass matrix utilized.
U.S. Pat. No. 5,281,380 discloses a fiber reinforced elastic sheet in which staples are oriented in the vertical direction of the sheet. Staple material, such as Nylon 66, is mixed into thermoplastic material and extruded through a molding die. The molding die includes a weir portion which is said to initially orients the fibers in the flow direction. Downstream from the weir portion is a flow passage which has a dimension at least twice that of the weir portion. After passing through the weir portion, the flow direction is changed, thereby changing the fiber
orientation with respect to the sheet surface. The sheet so formed can then be further processed for an intended application.
The present invention provides methods and apparatuses for orienting short fibers (fibers having a length of 0.1 microns to 10.sup.3 microns) in a composite article formed by injection molding a molding compound comprising a fiber/elastomeric material blend. The fibers utilized are known as "short fibers" in the art and have a length considerably shorter than the 0.5 inch (1.2 cm) length of short fibers of the U.S. Pat. No. 5,156,907 patent discussed in above.